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Last Updated: November 21, 2017 05:50 AM


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Circuits Designed by Dave Johnson, P.E. :

DC Current Indicator 6The circuit below is a simple way to indicate when DC current is flowing through a wire.  The circuit is designed so it will turn on a LED indicator light, whenever the voltage drop across a shunt resistor exceeds about 0.1volts.  The value of the resist. . . Circuit by Dave Johnson P.E.-October, 2005

Demo of a Wave Power Generator SystE - MAn inexpensive stepper motor is used as a voltage generator in this wave generator demo. . . . Hobby Circuit designed by Dave Johnson P.E.-March, 2007

Door Knob AlarmMany companies offer simple alarm devices for personal use in bedrooms or hotel rooms.  A metal chain attached to a box holding the electronics is placed around the inside doorknob of a wood door.  Anyone grabbing the knob from the outside is detected. . . Circuit by David A. Johnson P.E.-May, 2000

Door Knock BeeperIn some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door.  The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door. . . Circuit by David Johnson P.E.-June, 2009

Doorbell heard in BasementIf you can't hear your doorbell when you are in your basement try this circuit.  This circuit takes advantage of the 24vac power source located near the furnace.  Using a simple current transformer technique, the circuit sounds a beeper whenever the . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

DVD Recorder + TV Camera Make Cheap Data LoggerSometimes recording the results of a test requires as much ingenuity as designing the product.  Consider a situation which requires the collection of many different variables over a long period of time . . . Hobby Circuit designed by Dave Johnson P.E.-April, 2005

Daniel Was an Extremely Calculating Individual -  20-Mar-06 -Design News:   Some of us remember the "good old days" when we banged out design calculations on a high-end TI or HP scientific calculator.  And how we even wrote code to automate the calculations we repeated often! Thinking how cool it would be to do that again on a calculator he built himself, Daniel decided to __ Gadget Freak-Case # 12

DC Current Indicator 6 -  The circuit below is a simple way to indicate when DC current is flowing through a wire.  The circuit is designed so it will turn on a LED indicator light, whenever the voltage drop across a shunt resistor exceeds about 0.1volts.  The value of the resist. . . Circuit by Dave Johnson P.E.-October, 2005

Decision maker -  No circuit description, schematic only__ CdS Electronic

Deer Repellent -  Here is a simple sensor which can detect the seismic vibrations caused by a person or large animal walking nearby.  A representative application for the sensor is a deer repellent for the vegetable garden __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Demo of a Wave Power Generator SystE - M -  An inexpensive stepper motor is used as a voltage generator in this wave generator demo. . . . Hobby Circuit designed by Dave Johnson P.E.-March, 2007

Device Detects Hot Dogs -  3-Jun-14 -Design News:   Cabe AtwellIt's that time of the year.  You know, that time when the sun is beaming and all you want to do is spend the months outside with your dog.  Did you know that dogs can fall victim to heat stroke when the temperatures soar? Even with that coat insulator! Japanese firm Petline has created a new product __ Gadget Freak

Device Will Never Let You Forget Your Password -- it's Your Heartbeat -  13-Nov-14 -Design News:   Elizabeth MontalbanoBiometric identification for access to devices is nothing new, but a Canadian company has put a new spin on the technology by using peopleís heartbeats to allow them to wirelessly access their devices -- including their smartphone, computer, car, or even their home.  Bionym , founded in 2011 as a __ Gadget Freak

Dick Had a Cameo Role in Scream 2 -  23-Oct-06 -Design News:   Give the little witches and warlocks a real trick when they come clamoring for treats on Halloween with this doorbell-activated soundtrack.  All that's required to build this spooky sound generator is a moderate hack of a cassette player, which involves opening the case and rewiring the motor for __ Gadget Freak-Case #102

Dick Keeps His Home Fires Burning -  11-Dec-06 -Design News:   Give your Christmas lighting a country look and make your Nativity scene more realistic with an electronic flame flicker.  This device can be used as a lamp dimmer or a flame flicker simulator, and may be switched on and off with the switch on a lamp.  The flicker dynamics may be customized for __ Gadget Freak-Case #95

Dick Worked theGraveyard Shift -  9-Oct-06 -Design News:   When the local church needed storm effects for a skit, sound man Dick Neubert found the thunder on the Internet and added "lightning" with a photoflash strobe.  He used an uncommitted output from the mixing board to trigger the strobe with the sound signal via a simple interface.  The strobe places __ Gadget Freak-Case #91

Digital Game Show Timer -  Several Game Show timers included, scroll to find this one.  Using only two CMOS IC packages, this game show buzzer performs well enough to be on TV! The first contestant to press his button locks out the other two contestants.  The design is completely asynchronous and "fair".  Other logic families will also work and any appropriate power supply is fine.  For simplicity, a single-chime doorbell is used for the aural indicator.  If a buzzer is preferred, use double pole pushbuttons with the second poles connected to activate the buzzer.  Simply connecting a buzzer in place of the doorbell will work but the buzzer will sound until the reset switch is pushed.   __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Digital Motor Speed Regulator -  Andrew Morris had a problem with a small rotary tool built in China.  The tool fit nicely in the hand and was useful for precision cutting, drilling, and polishing.  Yet for delicate work, the tool was in bad need of a speed regulator.  Andrew had developed an analog motor speed regulator back in the mid-1990s, but this time, he wanted the benefits of a digital regulator.  The digital version was just as efficient, but it was less expensive to build and easier to assemble.  The digital circuit also provided more torque. 
 __ Designed by Andrew Morris' Gadget Freak-Case #226

Digital Satellite Finder -  This article describes a tool that we can build ourselves to assist with aligning the satellite-TV dish without having to take our receiver outside.  We are proposing a signal strength measurement...__ Electronics Projects for You

Digitally Adjustable Dancing Lights -  You might have come across several types of adjustable dancing lights  (flickering LEDs) .  Most of them use presets  (variable resistors) to adjust the rate of switching.  Being a mechanical component, the...__ Electronics Projects for You

Dimmable LED Desk Lamp -  30-Nov-12 -Design News:   Andrew Morris designed a dimmable LED driver circuit that is simple and energy efficient.  He then installed the circuit into a portable fluorescent lamp. __ Designed by Andrew R. Morris, Gadget Freak-Case #230

Directional Speed Controller -  based on the rc speed controllerwith the addition of an astable, you get a stand alone controller.   __ Contact: P. Townshend EduTek Ltd

DIY Flexible Display -  23-Jan-14 -Design News:   Flexible displays are a hot topic, and my goal was to find a cheap and easy way to build one at home.  Normally, flexible displays refer to Oled or E Ink, but I created a working prototype of a flexible display that can be built at home without special equipment.  The prototype shows a seven-digit __ Gadget Freak-Case #250

DIY Stomp Box Enclosures  -  I get a challenge out of making something that cost me nothing or close to it.  While passing by a place that sells all kinds of aluminum I got the idea of using a piece of square aluminum tubing for a stomp box enclosure.  Cloning a circuit for a stomp box can be fairly simple but when you start to design it to fit in a box even the simplest design takes some thought and planning.  This might seem impractical when you can just go to a place like Radio Shack and buy a box.  Whenever I've done this I have rarely found a box that was just what I wanted for a stomp box.  There are some rare places where you can get boxes like "Small Bear Electronics" which is an excellent resource.   __ Designed by Jon Tirone, AKA John Fisher

Do You Have an Idea? It May Be Worth $500! -  11-Apr-07 -Design News:   All you backyard inventorsdo you have an idea? It may be worth $500! Hear me out, Design News is looking for new s and itís worth $500.  If you have a creative invention you think should be seen on the pages of Design News or on Designnews.com, we want to hear about it! E-mail our __ Gadget Freak

Do You Know How to Engineer, Modify, and Use Emergency Preparedness Systems? -  30-Mar-15 -Design News:   Ann R.  ThryftIf a major catastrophe strikes your area, will you be prepared? Do you have the right kind of technology in place for disasters typical in your region, like earthquake versus hurricane versus tornado, as well as the necessary tech, tools, and supplies common to all of them? Do you know how to __ Gadget Freak

Does LG's Watch Urbane Fit the Smartwatch Bill? -  2-Jun-15 -Design News:   The team at iFixit has been tearing down smartwatches like clockwork lately.  Its latest endeavor is LG's latest smart watch, the LG Watch Urbane.  At first glance, it looks like a regular, albeit sharp-looking wristwatch; will we be disappointed by what's inside? Let's find out, shall we? Click on __ Gadget Freak

Dog Caller -  Dog trainers use a whistle to call dogs.  But why blow that irritating, loud whistle when the dog can hear a sound inaudible to the humans? We the humans can hear...__ Electronics Projects for You

Don Secretly Dreamed of Building a Time Machine -  3-Nov-03 -Design News:   Weary of the varying time loss and gain of his mantle clock despite ongoing corrective measures, Don set out to modernize its time base-but added to the challenge by trying not to alter its original workings.  His nonintrusive design employs the primary and core of a low-power filament transformer __ Gadget Freak

Donald Had a SeriousDesign News-Gadget Freak  Case of Red Eye -  24-Oct-05 -Design News:   Donald liked to wow people with his PowerPoint presentations.  So he developed an easy circuit to modulate an audio signal  (CD player) and transmit it over a beam of light  (using a laser pointer) .  The receiver is a simple solar cell with a pre-amp transistor circuit connected to the "line-in" of an __ Gadget Freak

Doodle3D Prints Designs From 2D Drawings -  21-May-13 -Design News:   Cabe AtwellThere's more fun coming our way on the 3D printing news front, as The Netherlands-based tech company FabLab Amersfoort has developed a new device that serves as a sketching tool for creating a 3D-printed object out of a simple 2D doodle.  Called Doodle3D , the sketching tool provides users with both __ Video-Gadget Freak

Door Knob Alarm -  Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms.  A metal chain attached to a box holding the electronics is placed around the inside doorknob of a wood door.  Anyone grabbing the knob from the outside is detected. . . Circuit by David A. Johnson P.E.-May, 2000

Door knock Alarm with timer -  This low-cost circuit uses the piezoelectric element of a piezobuzzer as the input sensor.  The piezoelectric element plate is fixed at the centre of the door wing by using a cello tape.  Apply a small quantity of adhesive at the edges between the plate and the door.  Extend wires about 1-1.5 metres from the piezoelectric to the circuit.  

Door Knock Beeper -  In some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door.  The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door. . . Circuit by David Johnson P.E.-June, 2009

Doorbell heard in Basement -  If you can't hear your doorbell when you are in your basement try this circuit.  This circuit takes advantage of the 24vac power source located near the furnace.  Using a simple current transformer technique, the circuit sounds a beeper whenever the . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Door-Knock or Vibration Alarm -  This is a simple circuit that activates an alarm when there is a knock on the door or there are any vibrations due to movement of heavy goods or furniture.  The circuit uses readily available components.__ Electronics Projects for You

Dr. Seuss Themed TargetGame -  15-Aug-14 -Design News:   Colorado State University students Zachary Lund, Jake Butynski, Allison Steinauer, and Tessa Alford have created "One Shot Two Shot, Red Shot Blue Shot" -- a Dr.  Seuss themed target game where the objective is to get the most points with six shots from the gun.  Each game, a new, random, pattern __ Gadget Freak-Case #261

Drill Speed Controller V2 -  PWM controller derived from a ramp generator and comparatoralso drives lamps and other devices __ Contact: P. Townshend EduTek Ltd

Drink Delivery Vehicle -Inverted Pendulum -  17-Oct-14 -Design News:   The DDV-IP is an inverted pendulum driving machine.  DDV-IP stands for Drink Delivery VehicleInverted Pendulum.  The concept is a two-wheeled self-balancing robot that can deliver cold beverages to thirsty folks on hot summer days.  A wireless RF remote enables manual control of the device beyond __ Gadget Freak-Case #264

Drinking Water Alarm -  The State Jal Boards supply water for limited duration in a day.  Time of water supply is decided by the management and the public does not know the same.  In such...__ Electronics Projects for You

Duct Tape and Baling Wire! -  26-Apr-04 -Design News:   Whiz kids  (and Colorado State University engineering students) Curtis and Dennis built a cool learning toy that tests the user's knowledge of binary numbers.  A microcontroller generates a random 16-bit number that is converted to 8-bits and displayed in binary form using eight LEDs.  If the user's __ Gadget Freak

Dust Proved to be Deadly for Greg's Computer Fan -  4-Aug-03 -Design News:   Tired of replacing failed fan units on his computer, Greg came up with a new, liquid chip-cooling system that seals out dirt and dust.  Coolant is circulated by a free-floating internal blade, which is magnetically linked to a drive piece and electric motor.  Heat sinks mounted to the top plate __ Gadget Freak

DVD Recorder + TV Camera Make Cheap Data Logger -  Sometimes recording the results of a test requires as much ingenuity as designing the product.  Consider a situation which requires the collection of many different variables over a long period of time . . . Hobby Circuit designed by Dave Johnson P.E.-April, 2005

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Gadgets:  #'s - C        D - E        G - L        M - O        P - S        T - Z


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